Micromirror array having reduced gap between adjacent micromirrors of the micromirror array

ABSTRACT

A spatial light modulator is disclosed, along with a method for making such a modulator that comprises an array of micromirror devices. The center-to-center distance and the gap between adjacent micromirror devices are determined corresponding to the light source being used so as to optimize optical efficiency and performance quality. The micromirror device comprises a hinge support formed on a substrate and a hinge that is held by the hinge support. A mirror plate is connected to the hinge via a contact, and the distance between the mirror plate and the hinge is determined according to desired maximum rotation angle of the mirror plate, the optimum gap and pitch between the adjacent micromirrors. In a method of fabricating such spatial light modulator, one sacrificial layer is deposited on a substrate followed by forming the mirror plates, and another sacrificial layer is deposited on the mirror plates followed by forming the hinge supports. The two sacrificial layers are removed via the small gap between adjacent mirror devices with spontaneous vapor phase chemical etchant. Also disclosed is a projection system that comprises such a spatial light modulator, as well as a light source, condensing optics, wherein light from the light source is focused onto the array of micromirrors, projection optics for projecting light selectively reflected from the array of micromirrors onto a target, and a controller for selectively actuating the micromirrors in the array.

CROSS-REFERENCE TO RELATED APPLICATIONS

The current application is a divisional application of co-pending U.S.patent application Ser. No. 10/627,302 to Patel filed Jul. 24, 2003,which is a continuation-in-part of U.S. patent application Ser. No.10/613,379 to Patel filed Jul. 3, 2003, the subject matter of each beingincorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention is related generally to the art ofmicroelectromechanical systems, and, more particularly, to micromirrorarray devices comprising a plurality of micromirror devices for use indisplay systems.

BACKGROUND OF THE INVENTION

The present invention relates to spatial light modulators havingreflective micromirrors that are provided within a micromirror arrayfor, e.g., projection-type displays (or for steering light beams,maskless lithography and maskless micro array production). A simplifiedsuch display system is illustrated in FIG. 1. In its very basicconfiguration, display system 100 comprises light source 102, opticaldevices (e.g. light pipe 104, condensing lens 106 and projection lens108), display target 112 and spatial light modulator 110 that furthercomprises a plurality of micromirror devices (e.g. an array ofmicromirror devices). Light source 102 (e.g. an arc lamp) emits lightthrough the light integrator/pipe 104 and condensing lens 106 and ontospatial light modulator 110. The micromirrors of the spatial lightmodulator 110 are selectively actuated by a controller (e.g. asdisclosed in U.S. Pat. No. 6,388,661 issued May 14, 2002 incorporatedherein by reference) so as to reflect—when in their “ON” position—theincident light into projection optics 108, resulting in an image ondisplay target 112 (screen, a viewer's eyes, a photosensitive material,etc.). Generally, more complex optical systems, such as systemsemploying more than three spatial light modulators (each beingdesignated for modulating one of the three primary colors—red, green andred) are often used, especially in displaying applications for colorimages.

It is often desirable for the display system to have a bright image.Brighter images are made possible by a number of factors, including theoptical efficiency of the micromirror array itself (fill factor,diffraction, reflectivity of the mirrors, etc.) as well as the opticalefficiency of the projection system (light source, light loss viafilters and lenses, micromirror array optical efficiency, etc.). One wayof increasing the brightness of a projection display is to use a shorterarc length arc lamp. For example, an arc length of 0.7 mm or 1.0 mm hasa higher brightness than a lamp with an arc length of 1.3 mm or 1.6 mm,because the beam produced by smaller arc length lamps can be more easilypassed through an optical system.

However, using an arc lamp in a projection system preferably utilizes amicromirror array with preferred dimension. In particular, for an arclamp with a given arc length, it is desired for the spatial lightmodulator to have a large enough size—if the optical efficiency of theprojection system (or more specifically, the optical couplingefficiency, to which the brightness of images produced by the spatiallight modulator, of the light source to the array) is not to bedegraded. A large spatial light modulator, however, is notcost-effective due to many factors, such as higher costs inmanufacturing and optical elements (e.g. condensing and projectionlenses). In practical design of the display system and the spatial lightmodulator, the cost-effectiveness and the optical efficiency need to bebalanced—yielding an optimal size of the spatial light modulator.

The diameter of a micromirror array is proportional to the micromirrorpitch (defined as the center-to-center distance between adjacentmicromirrors) for a given resolution (defined as the number ofmicromirrors in the micromirror array) of the micromirror array. Given aspatial light modulator with optimum size, the micromirror pitch needsto be reduced if a higher resolution is desired. Because the mirrorpitch is a summation of the gap between adjacent micromirrors and thesize of the micromirror, reduction of the mirror pitch requiresreduction of the gap between adjacent micromirrors if fill factor (thepercentage of reflective area to total array size and measured by aratio of the mirror size to the pitch) is not to be lost.

Therefore, what is needed is a spatial light modulator having an arrayof micromirror devices and a method of making such a spatial lightmodulator that allows for higher resolutions while maintain the sameoptimum size.

SUMMARY OF THE INVENTION

In the present invention, both designs of micromirror arrays of spatiallight modulators and methods of making the same are provided. Thespatial light modulators allow for micromirror arrays having smalleroverall dimensions, while allowing for good resolution and opticalefficiency. Moreover, the spatial light modulator allows for higherresolutions and optical efficiency while maintaining the same dimensionof the micromirror array. In a number of embodiments of the invention,micromirror arrays are constructed having a pitch of 10.16 micrometersor less. In other embodiments, micromirror array designs includemicromirror arrays having a gap between adjacent micromirrors of 0.5micrometers or less, and in other embodiments the gap is from 0.1 to 0.5micrometer. In yet other embodiments, micromirrors are constructed thatdo not have symmetric ON and OFF positions. In still furtherembodiments, methods for making mirror arrays utilize spontaneous gasphase chemical etchants to provide mirrors having smaller than usualdimensions.

In an embodiment of the invention, a method is disclosed. The methodcomprises: depositing a first sacrificial layer on a substrate; formingan array of mirror plates on the first sacrificial layer, wherein a gapbetween the adjacent mirror plates of the mirror plate array is from0.15 to 0.5 micrometers; depositing a second sacrificial layer on themirror plates with a thickness from 0.5 to 1.5 micrometers; forming ahinge support on the second sacrificial layer for each mirror plate forsupporting the mirror plate; and removing at least a portion of one orboth of the first and the second sacrificial layers using a spontaneousvapor phase chemical etchant.

In another embodiment of the invention, a spatial light modulator isdisclosed. The spatial light modulator comprises: an array of mirrordevices formed on a substrate for selectively reflecting light incidenton the mirror devices, wherein each mirror device comprises: a mirrorplate for reflecting light; a hinge attached to the mirror plate suchthat the mirror plate can rotate relative to the substrate, wherein thehinge and the mirror plate are spaced apart from 0.5 to 1.5 micrometers;and a hinge support on the substrate for holding the hinge on thesubstrate; and wherein the adjacent mirror plates have a gap from 0.15to 0.5 micrometers.

In yet another embodiment of the invention, a spatial light modulator isdisclosed. The spatial light modulator comprises: an array of movablemirror plates formed on a substrate for selectively reflecting a lightbeam incident on the mirror plates, wherein adjacent mirror plates havea gap from 0.15 to 0.5 micrometers when the adjacent mirror plates areparallel to the substrate.

In yet another embodiment of the invention, a projector is disclosed.The projector comprises: a light source; a spatial light modulator thatfurther comprises: an array of mirror devices formed on a substrate forselectively reflecting light incident on the mirror devices, whereineach mirror device comprises: a mirror plate for reflecting light; ahinge attached to the mirror plate such that the mirror plate can rotaterelative to the substrate, wherein the hinge and the mirror plate arespaced apart from 0.5 to 1.5 micrometers; a hinge support on thesubstrate for holding the hinge on the substrate; and wherein adjacentmirror plates has a gap from 0.15 to 0.5 micrometers; and a condensinglens for directing light from the light source onto the spatial lightmodulator; and a projecting lens for collecting and directing lightreflected from the spatial light modulator onto a display target.

In yet another embodiment of the invention, a projector is disclosed.The projector comprises: a light source; and a spatial light modulatorthat further comprises: an array of movable mirror plates formed on asubstrate for selectively reflecting a light beam incident on the mirrorplates, wherein adjacent mirror plates have a gap from 0.15 to 0.5micrometers when the mirror plates are parallel to the substrate.

BRIEF DESCRIPTION OF DRAWINGS

While the appended claims set forth the features of the presentinvention with particularity, the invention, together with its objectsand advantages, may be best understood from the following detaileddescription taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 diagrammatically illustrates an exemplary display systememploying a spatial light modulator;

FIG. 2 is illustrates a exemplary spatial light modulator having anarray of micromirrors;

FIG. 3 is a diagram schematically showing the brightness of the producedimages by the micromirror array, the cost of fabricating the micromirrorarray and the value (defined as the brightness per cost) versus thediameter of the micromirror array;

FIG. 4 plots the variation of the pitch size with the diameter of themicromirror array at different resolutions;

FIG. 5 plots the variation of the illumination efficiency of themicromirror array device with the pixel pitch;

FIG. 6 a schematically illustrates a minimum gap defined by two adjacentmirror plates that rotate symmetrically;

FIG. 6 b schematically illustrates another minimum gap defined by twoadjacent mirror plates that rotate symmetrically, wherein the distancebetween the mirror plate and the hinge is less than that in FIG. 6 a;

FIG. 6 c schematically illustrates yet another minimum gap defined bytwo adjacent mirror plates that rotate asymmetrically, wherein thedistance between the mirror plate and the hinge is the same as that inFIG. 6 b;

FIG. 7 is a cross-section view of two adjacent micromirrors illustratingthe relative rotational positions of two adjacent mirror plates when onemicromirror is at the OFF state and the other one at the ON state;

FIG. 8 a illustrates an exemplary micromirror array according to anembodiment of the invention;

FIG. 8 b illustrates a micromirror device of the micromirror array ofFIG. 8 a;

FIG. 9 a illustrates another exemplary micromirror array according to anembodiment of the invention;

FIG. 9 b illustrates a micromirror device of the micromirror array ofFIG. 9 a;

FIG. 10 a through 10 c are cross-sectional view of the micromirrorduring an exemplary fabrication process;

FIG. 11 is a flow chart showing steps executed in an etching process forremoving sacrificial layers;

FIG. 12 is a block diagram showing major components used in the etchingprocess of FIG. 11; and

FIG. 13 is a cross-sectional view of a mirror device in the midst of anetching process.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the present invention, both designs of micromirror arrays of spatiallight modulators and methods of making the same are provided. Thespatial light modulators allow for micromirror arrays having smalleroverall diameters, while allowing for good resolution and opticalefficiency. Moreover, the spatial light modulator allows for higherresolutions and optical efficiency while maintaining the same overalldimensions of the micromirror array of the spatial light modulator.

According to the invention, the light source of the display system is anarc lamp with a short arc length preferably 1.6 millimeters or less,more preferably 1.3 millimeters or less, more preferably 1.0 millimetersor less. The power of the arc lamp is preferably from 100 watts to 250watts.

The dimension of the micromirror array and the spatial light modulatoris defined with reference FIG. 2. Spatial light modulator 110 comprisesan array of micromirrors that has m×n micromirrors (e.g. micromirrordevice 114), wherein m and n respectively represent the number ofmicromirror devices in a row and a column of the array. The micromirrorarray also has a well defined diagonal, which is generally measured ininches. As shown in the insert figure, a gap and pitch is defined by twoadjacent micromirrors. L_(plate) measures the size of the micromirror,and W_(post) measures the post area of the micromirror. The post area isthe area in which posts (e.g. post 219 in FIG. 8 b and FIG. 9 b) forholding the mirror plate are formed. Though the insert figureillustrates the dimensions of the micromirror and the adjacentmicromirrors with the micromirror of rectangular shape, those dimensiondefinitions are applicable to any micromirrors and micromirror arrays.

To be compatible with an arc lamp as the light source of the displaysystem, while satisfying the cost-effectiveness requirement, an optimumdiameter is determined for the micromirror array of the spatial lightmodulator. For example, in a display system using an arc lamp with anarc length around 1.0 mm, the brightness of images produced by thespatial light modulator modulating light from the arc lamp, the cost ofspatial light modulator and value (defined as the brightness per cost)versus the overall diameter of the spatial light modulator areillustratively plotted in FIG. 3. Referring to FIG. 3, brightness andcost are respectively plotted in dash-line and dotted-line withreference to the Y axis on the right side. The value is plotted insolid-line with reference to Y axis on the left side. As can be seenfrom the figure, brightness increases with the diameter of themicromirror array increasing and saturates after the diameter of themicromirror array is around 0.8 inch. As a simple approximation, thecost is linearly proportional to the diameter of the micromirror array.The value, defined as the brightness per cost, varies with the diameterof the micromirror array and presents a maximum value when the diameteris around 0.7 inch. According to the invention, the diameter of themicromirror array is preferably from 0.55 inch to 0.8 inch, morepreferably from 0.65 to 0.75 inch, and more preferably around 0.7 inch.

Given the diameter of a micromirror array within a spatial lightmodulator, the pitch (defined as the center-to-center distance betweenadjacent micromirrors) of the micromirror array depends upon theresolution of the micromirror array, which can be expressed as:$\begin{matrix}{{Pitch} = \frac{Diameter}{\sqrt{m^{2} + n^{2}}}} & \left( {{Eq}.\quad 1} \right)\end{matrix}$FIG. 4 illustrates the variation of the pitch versus diameter of themicromirror array at different resolutions. Referring to FIG. 4, opencircles, open squares, open triangles and solid circles respectivelyrepresents resolutions of 1280×720, 1400×1050, 1600×1200 and 1920×1080.It can be seen from the plot that, when the diameter is around 0.38inch, the optimum pitch sizes are from 4.38 to 6.57 μm with theresolution varying from 1920×1080 to 1280×720. When the diameter of themicromirror array is around 0.54 inch, the optimum pitch sizes are from6.23 to 9.34 μm with the resolution varying from 1920×1080 to 1280×720.When the diameter of the micromirror array is around 0.7 inch, theoptimum pitch sizes are from 8.07 to 12.11 μm with the resolutionvarying from 1920×1080 to 1280×720. And when the diameter of themicromirror array is around 0.86 inch, the optimum pitch sizes are from9.92 to 14.87 μm with the resolution varying from 1920×1080 to 1280×720.

The diameter of the micromirror array depends upon two dimensionalparameters—the diagonal of the mirror plate (L_(plate)) of themicromirror and the gap between adjacent micromirrors, as defined inFIG. 2. Of the two parameters, the gap degrades the optical efficiencyof the micromirror in reflecting light. This type of degradation can beanalyzed in terms of illumination efficiency, which is defined as theratio of the total effective reflective area to the total area of themicromirror array. Specifically, the illumination efficiency (eff) canbe expressed as: $\begin{matrix}{{eff} = \frac{\left( {{pitch} - {gap}} \right)^{2} - {2 \times W_{post}^{2}}}{{pitch}^{2}}} & \left( {{Eq}.\quad 2} \right)\end{matrix}$wherein the term (pitch-gap)²−2×W_(post) ² is the total effectivereflection area of the micromirrors of the micromirror array, and pitch²is the total area of the micromirrors of the micromirror array. FIG. 5plots the illumination efficiency versus the pitch size with the posthaving a fixed size (W_(post)=1.0 μm) and the gap having a size of 0.5μm, 0.25 μm and 0.15 μm. Specifically, the line with solid triangles,the line with solid circles and the line with solid circles respectivelyplot the dependency of the illumination efficiency upon the pixel pitchwhen the gap is 0.25 μm, 0.5 μm and 0.15 μm, and the post size is 0.5μm. From the figure, it can be seen that when the gap is around 0.25 μm,the pitch size of the micromirror array is at least 4.38 μm so as toobtain the illumination efficiency higher than 85%. And when the gap isaround 0.5 μm, the pitch size of the micromirror array is at least 8.07μm so as to obtain the illumination efficiency higher than 85%. If theillumination efficiency is desired to be higher than 90%, the pitch sizeis at least 4.38 μm, 6.23 μm and 10.16 μm when the gap size is around0.15 μm, 0.25 μm and 0.5 μm, respectively. In the present invention, thepitch size of the micromirror array device is preferably from 4.38 μm to10.16 μm, preferably from 4.38 μm to 9.34 μm, and preferably from 4.38μm to 6.57 μm, and preferably from 6.23 μm to 9.34 μm, and morepreferably from 8.07 μm to 10.16 μm. It is also preferred that the gapbetween adjacent micromirrors is 0.5 μm or less, more preferably, from0.25 μm to 0.5 μm, and more preferably from 0.15 μm to 0.25 μm.

As discussed above, in view of the optical efficiency andcost-effectiveness of the display system, the micromirror array withinthe spatial light modulator of the display system has an optimumdiameter. For a micromirror array with the optimum diameter, it isdesired to reduce the pitch size of the micromirror array in order toaccommodate more micromirrors—achieving higher resolutions. Because thepitch is a summation of the length of the micromirror and the gapbetween adjacent micromirrors, the reduction of the pitch can beachieved by either reducing the micromirror size or the gap betweenadjacent micromirrors. Reduction of the micromirror size withoutreducing the gap size, however, damages the illumination efficiency ofthe micromirror array, as discussed with reference to FIG. 5. Therefore,reduction of the gap, as well as reduction of the mirror size, is alsopreferred in achieving higher resolution for a micromirror array withthe given optimum diameter. Though reduction of the pitch can beachieved by reducing the gap size and the mirror size, the gap size andthe mirror size do not have to both be reduced. In particular, reductionof the gap is preferred to achieve a small pitch if it is achievable. Ifthe desired small pitch is not achievable by reducing the gap only,mirror size is reduced.

In order to allow for reduction of the gap between adjacent micromirrorsof the micromirror array, the micromirror of the present invention isdesigned such that the mirror plate of the micromirror rotatesasymmetrically along a rotation axis, because asymmetric rotation allowsfor a smaller gap than the symmetric rotation. Moreover, the distancebetween the mirror plate and the rotation axis is as small as comparedto the distance between the mirror plate and the substrate on which themirror plate is formed. Detailed embodiments will be discussed in thefollowing with reference to FIG. 6 a, FIG. 6 b and FIG. 6 c. As anoptional feature of the invention, such asymmetry aids in achievingsmaller pitch and gap micromirror arrays without adjacent micromirrorsimpacting each other.

FIG. 6 a illustrates a cross-sectional view of two adjacentmicromirrors, each rotating symmetrically. The solid dark circle in eachmicromirror represents the rotation axis of the mirror plate. Pitch₁measures the pitch (equal to the distance between the two rotation axes)between the adjacent micromirrors. t_(sac) is the distance between themirror plate and the rotation axis. The trajectory of the ends of eachmirror plate is plotted in dotted circle. The micromirror 2 is fixed andits mirror plate is rotated clockwise to the OFF state anglecorresponding to the OFF state of the micromirror. The micromirror 1 canbe fabricated to be closer or further away from micromirror 2. And thepitch₁ is thus variable. In the figure, the micromirror 1 is placed at aposition such that during the counter-clockwise rotation of the mirrorplate of the micromirror 1 towards the ON state angle, the “right” endof the mirror plate is tangent but without impacting to the “left” endof the mirror plate of the micromirror 2. From this situation, gap₁ isdefined by the two mirror plates of the two adjacent micromirrors whenthey are “flat” (e.g. parallel to the substrate or non-deflected).

FIG. 6 b illustrates a cross-sectional view of two adjacentmicromirrors, each rotating symmetrically, while the distance t_(sac2)between the mirror plate and the rotation axis is smaller than that inFIG. 6 a, that is t_(sac2)<t_(sac1). By comparing the gaps and pitchesin FIG. 6 a and FIG. 6 b, it can be seen that gap₂<gap₁, andpitch₂<pitch₁. That is, the smaller t_(sac2) allows for a smaller gapand smaller pitch micromirror array.

The gap and the pitch between adjacent micromirrors in FIG. 6 b can bemade even smaller by attaching the mirror plate to the hingeasymmetrically, as shown in FIG. 6 c. Referring to FIG. 6 c, across-sectional view of two adjacent micromirrors, each being attachedto the hinge such that he mirror plate rotates asymmetrically along therotation axis, is illustrated therein. Specifically, each mirror plateis attached to the hinge, and the attachment point is positioned closerto one end of the mirror plate than the other. For example, theattachment point of the mirror plate of the micromirror 1 is positionedaway from the “right” end A of the mirror plate. And the attachmentpoint of the mirror plate of the micromirror 2 is positioned towards the“left” end B of the micromirror 2. The mirror plates are otherwiseidentical to those in FIG. 6 a and FIG. 6 b (e.g. the distance betweenthe mirror plate and the rotation axis in FIG. 6 c is the same as thatin FIG. 6 b). The trajectories of the end A and end B of the mirrorplates are plotted in dotted circles. Because the rotations of themirror plates along their rotation axes are asymmetrical, the trajectorycircles of the end A and end B are different. By comparing the gaps andthe pitches in FIG. 6 b and FIG. 6 c, it can be seen that gap₃ andpitch₃ in FIG. 6 c are smaller than those in FIG. 6 b and FIG. 6 a. Inparticular, gap₃<gap₂<gap₁, and pitch₃<pitch₂<pitch₁. Though a smalldistance between the mirror plate and the rotation axis and anasymmetric rotation are not required in the present invention, they aidin the ability to achieve small pitch and small gap micromirrorarrays—particularly at the lower ends of the dimension ranges in thepresent invention.

Referring to FIG. 7, a cross-sectional view of two adjacent micromirrorsis illustrated therein. The mirror plates (e.g. mirror plate 116) of themicromirrors each rotates asymmetrically along a rotation axis.Specifically, the mirror plate (e.g. mirror plate 116) is attached to ahinge (e.g. hinge 120) via a hinge contact (e.g. hinge contact 118). Thedistance between the mirror plate and the hinge is denoted by t_(sac).As can be seen from the figure, the mirror plate is attached to thehinge asymmetrically. Specifically, the attachment point of the mirrorplate to the hinge contact is extended towards one end of the mirrorplate so as to enabling the mirror plate to rotate asymmetrically to anON state or an OFF state. The ON state is defined as a state whereinlight reflected by the mirror plate is collected by the projection lens(e.g. projection lens 108 in FIG. 1) and generating a “bright” pixel ofan image on the display target (e.g. display target 112 in FIG. 1). TheOFF state is defined as a state wherein light is reflected by the mirrorplate away from the projection lens—resulting in a “dark” pixel on thedisplay target.

The ON state angle and the OFF state angle affect the quality of theproduced image, such as the contrast ratio of the image. To obtain ahigh contrast ratio, a large ON state angle corresponding to the ONstate and a non-zero OFF state angle corresponding to the OFF state arepreferred. Specifically, it is preferred than the ON state angle is from12° degrees to 18° degrees, and the OFF state angle is from −2° degreesto −8° degrees, wherein the “+” and “−” signs represent oppositerotation directions of the mirror plate as shown in the figure.

The ON state rotation angle and the OFF state rotation angle areachieved by applying an electrostatic force to the mirror plate andproviding stop mechanisms for stopping the rotation of the mirror plateswhen the mirror plate rotates to the ON state angle or the OFF stateangle. For example, the stop mechanism can be a substrate (e.g.substrate 210 in FIG. 8 b) on which the mirror plate is formed ordesignated stops (e.g. stop 216 in FIG. 8 b). In either case, a smalldistance between the mirror plate and the hinge is desired to benefitlarge rotation angle for the ON state and a small rotation angle for theOFF state. According to the invention, the distance between the mirrorplate and the hinge is preferably from 0.15 to 0.45 micrometers, e.g.from 0.15 to 0.25 micrometers, or from 0.25 to 0.45 micrometers. Largerdistance between the mirror plate and the hinge could also be used, suchas a distance from 0.5 to 1.5 micrometers, or from 0.5 to 0.8micrometers, or from 0.8 to 1.25 micrometers, or from 1.25 to 1.5micrometers.

Referring to FIG. 8 a, an exemplary micromirror array device 110 isillustrated therein. The micromirror array device comprises m×nmicromirrors, wherein m and n respectively represents the number ofmicromirrors in a row and the number of micromirrors in a column of thearray. The values of m and n determine the resolution of the displayedimages. In the embodiment of the invention, the m×n are preferably1280×720, 1400×1050, 1600×1200, 1920×1080, 2048×1536 or higher. Adjacentmicromirrors in a row or a column of the micromirror array define a gaptherebetween. The gap determines the fill factor of the micromirrorarray device, wherein the fill factor is defined as the ratio of thetotal area of the mirror plates of the micromirrors to the area of themicromirror array. For example, the fill factor can be calculated by:the area of a micromirror plate of the micromirror divided by the pitchsquared, provided that the mirror plates of the micromirrors areidentical and the pitch size is uniform over the entire micromirrorarray. In an embodiment of the invention, the fill factor of themicromirror array device is 85% or higher, and more preferably, 90% orhigher. Proximate to micromirror array 220, electrode array 225 isdisposed for selectively actuating the micromirrors. For example, anelectrostatic field is established between the selected micromirror andthe electrode disposed proximate to and designated for rotating theselected micromirror. In response to the electrostatic field, themicromirror rotates relative to substrate 210 to either an ON state oran OFF state (if the OFF state is defined as the micromirror having anangle with substrate 210) such that light incident onto the selectedmicromirror through substrate 210 can be reflected either into or awayfrom a projection lens (e.g. projection lens 108 in FIG. 1 a).

In this particular example, the micromirrors are formed on substrate210, such as quartz or glass that is transmissive to visible light. Andthe electrode array is formed on substrate 215, which is a standardsemiconductor wafer. In addition to the electrode array, a circuitarray, such as a DRAM or SRAM array is also formed on substrate 215.Each circuit maintains a voltage signal and is connected to oneelectrode such that the voltage of the electrode is defined by thevoltage signal in the circuitry. In this way, the electrostatic fieldbetween the mirror plate and the electrode is controlled by the circuit.

FIG. 8 b schematically illustrates a back-view of a micromirror ofmicromirror array 110. As can be seen, the micromirror comprises mirrorplate 212, hinge 222, hinge contact 224 and hinge support 218. Themirror plate is connected to the hinge through the contact. And thehinge is affixed to the hinge support that is formed on substrate 210.It is noted that the mirror plate is attached to the hinge such that themirror plate can rotate relative to the substrate along a rotation axisthat is parallel to but offset from a diagonal of the mirror plate whenviewed from the top of the substrate. By “parallel to but offset fromthe diagonal”, it is meant that the axis of rotation can be exactlyparallel to or substantially parallel to (±19 degrees) the diagonal ofthe micromirror but offset from the diagonal when viewed from the above.With this configuration, the mirror plate is able to rotateasymmetrically along the rotation axis in two opposite rotationdirections and achieves a large ON state angle compared to the ON stateangles achieved by those micromirrors rotating symmetrically. In thepresent invention, the ON state angle is preferably +12° degrees ormore, preferably +16° degrees or more, preferably +18° degrees or moreand more preferably +20° degrees or more. And the OFF state angle ispreferably from −1° degree to −8° degrees, and preferably around −4°degrees. In addition to the hinge and the contact, other features mayalso be formed on the hinge support. For example, stops 216 and 217 canbe formed on the hinge support for stopping rotations of the mirrorplate when the mirror plate achieves the ON state and OFF state angles.Specifically, stop 216 and stop 217 are respectively designated forstopping the mirror plate in rotating in a direction towards the ONstate and in another direction towards the OFF state. By properlysetting the length and the positions of the mirror stops and thedistance between the mirror plate and the hinge, the ON state angle andthe OFF state angle of all micromirrors can be uniformly achieved. Theuniform OFF state angle and the ON state angle certainly improves thequality of performance of the micromirror array device. The qualities ofthe displayed images are improved.

The mirror plate rotates in response to an electrostatic field betweenthe mirror plate and the electrode associated with the mirror plate.Specifically, an electrode is associated with the mirror plate fordriving the mirror plate to rotate to the ON state. When the OFF stateof the micromirror corresponds to a non-zero OFF state angle, a separateelectrode (not shown) can be provided. The second electrode can beplaced in any suitable location as along as it drives the mirror plateto rotate to the non-zero OFF state angle. For example, the secondelectrode can be placed on the same substrate as the first electrode forthe ON state is disposed, but at a location on the opposite side of therotation axis of the mirror plate. For another example, the secondelectrode can be disposed on the opposite side of the mirror plate inrelation to the first electrode for the ON state. Alternative to formingthe second electrode on the same substrate as the first electrode forthe ON state being formed, the second electrode can be formed on theglass substrate, on which the micromirrors are formed. In this case, thesecond electrode is preferably an electrode grid, or electrode frame (orsegments, such as stripes) below each micromirror. The second electrodecan also be formed as an electrode film on the surface of the glasssubstrate, in which case, the electrode film is transparent to visiblelight. In addition to being used as electrode for driving the mirrorplate to rotate, the second electrode on the glass substrate can also beused as light absorbing grid (or frame or segments) or anti-reflectionfilm. Alternatively, the OFF state corresponding to the non-zero OFFstate angle can be achieved without the second electrode. For example, aportion of the hinge structure can be made such that the portion iscurved away from parallel to the substrate at the natural resting state.The mirror plate, which is attached to the curved portion present anangle to the substrate at the natural resting state.

Referring to FIG. 9 a and FIG. 9 b, another exemplary micromirror arraydevice and micromirror are illustrated therein. As seen in FIG. 9 b, theshape of the mirror plate, shape of the hinge structure and relativearrangement of the mirror plate and the hinge structure of themicromirror are different from those in FIG. 8. In fact, the micromirrorand the micromirror array of the micromirror array device can take manysuitable forms. For example, the micromirrors and the electrodes of themicromirror array device can be formed on the same substrate (e.g.substrate 210 in FIG. 9 a). And more than one electrode can be disposedproximate to each micromirror for rotating the mirror plate of themicromirror. In this case, at least one electrode is designated fordriving the mirror plate to rotate in a first rotational direction, andat least another electrode is designated for driving the mirror plate torotate in a second rotational direction that is opposite to the firstrotation direction.

There is a variety of ways to construct the micromirror device describedabove, such as the fabrication methods disclosed in U.S. Pat. Nos.5,835,256 and 6,046,840 both to Huibers, the subject matter of eachbeing incorporated herein by reference. Regardless of the fabricationprocess, sacrificial materials are deposited between structures of themicromirrors and removed afterwards. For example, a sacrificial materialis deposited between the mirror plate and the hinge to which the mirrorplate is attached. The order of the fabrication steps for the mirrorplate and the hinge depends upon the selected fabrication process andother factors, such as substrate. In particular, the mirror plate can befabricated before the hinge, and alternatively, it can be fabricatedafter the hinge. For example, when the substrate is a silicon wafer, thehinge is fabricated before the mirror plate on the silicon wafer. Foranother example, when a glass substrate that is transmissive to visiblelight is used, the mirror plate is then fabricated before fabricatingthe hinge on the glass substrate. The sacrificial material also fillsthe space, such as gaps between adjacent micromirrors of the micromirrorarray. Removal of those sacrificial materials, however, is not a trivialprocess. As discussed earlier, the size of the gap between the hinge andthe mirror plate is preferably from 0.15 to 0.45 microns, although thedistance between the mirror plate and the hinge can be 0.15 to 1.5microns according to the present invention. In order to efficientlyremove sacrificial materials between the structures of the micromirrors,a spontaneous vapor phase chemical etching process is employed, whichwill be described in the following discussion on an exemplaryfabrication process.

A demonstrative fabrication process for making the micromirror and themicromirror array device of the present invention will be discussed inthe following with references to FIG. 10 a through FIG. 10 c. U.S.patent application Ser. No. 09/910,537 filed on Jul. 20, 2001 and60/300,533 filed on Jun. 22, 2001 both to Reid contain examples of thematerials that may be used for the various components of the presentinvention. These patent applications are also incorporated herein byreference. It should be appreciated by those of ordinary skill in theart that the exemplary processes are for demonstration purpose only andshould not be interpreted as limitations. In particular, although notlimited thereto, the exemplary micromirror is formed on a glasssubstrate that is transparent to visible light. And electrode andcircuitry are formed on a separate substrate, such as a silicon wafer.Alternatively, the micromirror and the electrode and circuitry can beformed on the same substrate.

Referring to FIG. 10 a, a cross-section view of a micromirror FIG. 8 bduring an exemplary fabrication process is illustrated therein. Themicromirror is formed on substrate 210, which can be glass (e.g. 1737F,Eagle 2000, quartz, Pyrex™, sapphire) that is transparent to visiblelight. First sacrificial layer 240 is deposited on substrate 210followed by forming mirror plate 232. First sacrificial layer 240 may beany suitable material, such as amorphous silicon, or could alternativelybe a polymer or polyimide, or even polysilicon, silicon nitride, silicondioxide and tungsten, depending upon the choice of sacrificialmaterials, and the etchant selected. In the embodiment of the invention,the first sacrificial layer is amorphous silicon, and it is preferablydeposited at 300-350° C. The thickness of the first sacrificial layercan be wide ranging depending upon the micromirror size and desiredtitle angle of the micro-micromirror, though a thickness of from 500 Åto 50,000 Å, preferably close to 25,000 Å, is preferred. The firstsacrificial layer may be deposited on the substrate using any suitablemethod, such as LPCVD or PECVD.

As an optional feature of the embodiment, an anti-reflection film maybedeposited on the surface of substrate 210. The anti-reflection film isdeposited for reducing the reflection of the incident light from thesurface of the substrate. Of course, other optical enhancing films maybe deposited on either surface of the glass substrate as desired. Inaddition to the optical enhancing films, an electrode may be formed on asurface of substrate 210. The electrode can be formed as an electrodegrid or a series of electrode segments (e.g. electrode strips) aroundthe mirror plate. Alternatively, the electrode can be formed as anelectrode film on the surface of substrate 210, in which case, theelectrode film is transparent to visible light. The electrode can beused for driving the mirror plate to either the ON state or the OFFstate. Alternatively, a light absorbing grid can be deposited on asurface of the glass substrate and around or below each micromirror. Thelight absorbing frame absorbs light incident onto and/or scattered lightfrom the edges of the micromirrors. The absorption of the scatteredlight improves the quality of performance, such as contrast ratio, ofthe micromirror.

After depositing the first sacrificial layer, mirror plate 232 isdeposited and patterned on the first sacrificial layer. Because themicromirror is designated for reflecting incident light in the spectrumof interest (e.g. visible light spectrum), it is preferred that themicromirror plate layer comprises of one or more materials that exhibithigh reflectivity (preferably 90% or higher) to the incident light. Thethickness of the micromirror plate can be wide ranging depending uponthe desired mechanical (e.g. elastic module), the size of themicromirror, desired ON state angle and OFF state angle, and electronic(e.g. conductivity) properties of the mirror plate and the properties ofthe materials selected for forming the micromirror plate. According tothe invention, a thickness from 500 Å to 50,000 Å, preferably around2500 Å, is preferred for the mirror plate. In an embodiment of theinvention, mirror plate 232 is a multi-layered structure, whichcomprises a SiO_(x) layer with a preferred thickness around 400 Å, alight reflecting layer of aluminum with a preferred thickness around2500 Å, a titanium layer with a preferred thickness around 80 Å, and a200 Å TiN_(x) layer. In addition to aluminum, other materials, such asTi, AlSiCu and TiAI, having high reflectivity to visible light can alsobe used for the light reflecting layer. These mirror plate layers can bedeposited by PVD at a temperature preferably around 150° C.

After deposition, mirror plate 232 is patterned into a desired shape,such as that in FIG. 8 b or FIG. 9 b. The patterning of the micromirrorcan be achieved using standard photoresist patterning followed byetching using, for example CF4, C12, or other suitable etchant dependingupon the specific material of the micromirror plate layer.

After patterning mirror plate 232, second sacrificial layer 242 isdeposited on the mirror plate 232 and first sacrificial layer 240. Thesecond sacrificial layer may comprise amorphous silicon, or couldalternatively comprise one or more of the various materials mentionedabove in reference to the first sacrificial layer. First and secondsacrificial layers need not be the same, although they are the same inthe preferred embodiment so that, in the future, the etching process forremoving these sacrificial materials can be simplified. Similar to thefirst sacrificial layer, the second sacrificial layer may be depositedusing any suitable method, such as LPCVD or PECVD. In the embodiment ofthe invention, the second sacrificial layer comprises amorphous silicondeposited at approximate 350° C. The thickness of the second sacrificiallayer can be on the order of 12,000 Å, but may be adjusted to anyreasonable thickness, such as between 2,000 Å and 20,000 Å dependingupon the desired distance (in the direction perpendicular to themicromirror plate and the substrate) between the micromirror plate andthe hinge. It is preferred that the hinge and mirror plate be separatedby a gap with a size from 0.1 to 1.5 microns, more preferably from 0.1to 0.45 micron, and more preferably from 0.25 to 0.45 microns. Largergaps could also be used, such as a gap from 0.5 to 1.5 micrometers, orfrom 0.5 to 0.8 micrometer, or from 0.8 to 1.25 micrometers, or from1.25 to 1.5 micrometers.

In the preferred embodiment of the invention, the micromirror platecomprises aluminum, and the sacrificial layers (e.g. the first andsecond sacrificial layer) are amorphous silicon. This design, however,can cause defects due to the diffusion of the aluminum and silicon,especially around the edge of the mirror plate. To solve this problem, aprotection layer (not shown) maybe deposited on the patternedmicromirror plate before depositing the second sacrificial silicon layersuch that the aluminum layer can be isolated from the siliconsacrificial layer. This protection may or may not be removed afterremoving the sacrificial materials. If the protection layer is not to beremoved, it is patterned after deposition on the mirror plate.

The deposited second sacrificial layer is then patterned for forming twodeep-via areas 248 and shallow via area 246 using standard lithographytechnique followed by etching, as shown in the figure. The etching stepmay be performed using Cl₂, BCl₃, or other suitable etchant dependingupon the specific material(s) of the second sacrificial layer. Thedistance across the two deep-via areas depends upon the length of thedefined diagonal of the micromirror plate. In an embodiment of theinvention, the distance across the two deep-via areas after thepatterning is preferably around 10 μm, but can be any suitable distanceas desired. In order to form the shallow-via area, an etching step usingCF₄ or other suitable etchant may be executed. The shallow-via area,which can be of any suitable size, is preferably on the order of 2.2square microns. And the size of each deep-via is approximate 1.0 micron.

After patterning the second sacrificial layer, hinge structure layer 250is deposited on the patterned second sacrificial layer. Because thehinge structure is designated for holding the hinge (e.g. hinge 222 inFIG. 8 b) and the micromirror plate (e.g. mirror plate 232 in FIG. 8 b),it is desired that the hinge structure layer comprises of materialshaving at least large elastic modulus. According to an embodiment of theinvention, hinge structure layer 250 comprises a 400 Å thickness ofTiN_(x) (although it may comprise TiN_(x), and may have a thicknessbetween 100 Å and 2000 Å) layer deposited by PVD, and a 3500 Å thicknessof SiN_(x) (although the thickness of the SiNx layer may be between 2000Å and 10,000 Å) layer 350 deposited by PECVD. Of course, other suitablematerials and methods of deposition may be used (e.g. methods, such asLPCVD or sputtering). The TiN_(x) layer is not necessary for theinvention, but provides a conductive contact surface between themicromirror and the hinge in order to, at least, reduce charge-inducedstiction.

After the deposition, hinge structure layer 250 is patterned into adesired configuration, such as hinge structure 218 in FIG. 8 b. Anetching step using one or more proper etchants is executed in patterningthe hinge structure layer. In particular, the layer can be etched with achlorine chemistry or a fluorine chemistry where the etchant is aperfluorocarbon or hydrofluorocarbon (or SF₆) that is energized so as toselectively etch the hinge support layers both chemically and physically(e.g. a plasma/RIE etch with CF₄, CHF₃, C₃F₈, CH₂F₂, C₂F₆, SF₆, etc. ormore likely combinations of the above or with additional gases, such asCF₄/H₂, SF₆/Cl₂, or gases using more than one etching species such asCF₂Cl₂, all possibly with one or more optional inert diluents).Different etchants may, of course, be employed for etching each hingesupport layer (e.g. chlorine chemistry for a metal layer, hydrocarbon orfluorocarbon (or SF₆) plasma for silicon or silicon compound layers,etc.).

Referring to FIG. 10 b, after patterning the hinge structure layer, thebottom segment of contact area 236 is removed and part of themicromirror plate underneath the contact area is thus exposed to hingelayer 238, which is deposited on the patterned hinge structure layer, toform an electric-contact with external electric source. The sidewalls ofcontact area 236 are left with residues of the hinge structure layersafter patterning. The residue on the sidewalls helps to enhance themechanical and electrical properties of the hinge. Each of the twodeep-via areas 234 on either side of the mirror can form a continuouselement with the deep-via areas corresponding to the adjacentmicromirror in an array.

In the embodiment of the invention, the hinge layer is also used as anelectric contact for the micromirror plate. It is desired that thematerial of the hinge layer is electrically conductive. Examples ofsuitable materials for the hinge layer are silicon nitride, siliconoxide, silicon carbide, polysilicon, Al, Ir, titanium, titanium nitride,titanium oxide(s), titanium carbide, CoSiN_(x), TiSiN_(x), TaSiN_(x), orother ternary and higher compounds. When titanium is selected for thehinge layer, it can be deposited at 100° C. Alternatively, the hingelayer may comprise of multi-layers, such as 100 Å TiN_(x) and 400 ÅSiN_(x).

After deposition, the hinge layer is then patterned as desired usingetching. Similar to the hinge structure layer, the hinge layer can beetched with a chlorine chemistry or a fluorine chemistry where theetchant is a perfluorocarbon or hydrofluorocarbon (or SF₆) that isenergized so as to selectively etch the hinge layers both chemically andphysically (e.g. a plasma/RIE etch with CF₄, CHF₃, C₃F₈, CH₂F₂, C₂F₆,SF₆, etc. or more likely combinations of the above or with additionalgases, such as CF₄/H₂, SF₆/Cl₂, or gases using more than one etchingspecies such as CF₂Cl₂, all possibly with one or more optional inertdiluents). Different etchants may, of course, be employed for etchingeach hinge layer (e.g. chlorine chemistry for a metal layer, hydrocarbonor fluorocarbon (or SF₆) plasma for silicon or silicon compound layers,etc.).

After the hinge is formed, the micromirror is released by removing thesacrificial materials of the first and second sacrificial layers, whichwill be discussed in detail in the following with reference to FIG. 11and FIG. 12. A cross-sectional view of the released micromirror deviceis presented in FIG. 10 c.

In order to efficiently remove the sacrificial material (e.g. amorphoussilicon), the release etching utilizes an etchant gas capable ofspontaneous chemical etching of the sacrificial material, preferablyisotropic etching that chemically (and not physically) removes thesacrificial material. Such chemical etching and apparatus for performingsuch chemical etching are disclosed in U.S. patent application Ser. No.09/427,841 to Patel et al. filed Oct. 26, 1999, and in U.S. patentapplication Ser. No. 09/649,569 to Patel at al. filed Aug. 28, 2000, thesubject matter of each being incorporated herein by reference. Preferredetchants for the release etch are gas phase fluoride etchants that,except for the optional application of temperature, are not energized.Examples include HF gas, noble gas halides such as xenon difluoride, andinterhalogens such as IF₅, BrCl₃, BrF₃, IF₇ and ClF₃. The release etchmay comprise inner gas components such as (N₂, Ar, Xe, He, etc.). Inthis way, the remaining sacrificial material is removed and themicromechanical structure is released. In one aspect of such anembodiment, XeF₂ is provided in an etching chamber with diluents (e.g.N₂ and He). The concentration of XeF₂ is preferably 8 Torr, although theconcentration can be varied from 1 Torr to 30 Torr or higher. Thisnon-plasma etch is employed for preferably 900 seconds, although thetime can vary from 60 to 5000 seconds, depending on temperature, etchantconcentration, pressure, quantity of sacrificial material to be removed,or other factors. The etch rate may be held constant at 18 Å/s/Torr,although the etch rate may vary from 1 Å/s/Torr to 100 Å/s/Torr. Eachstep of the release process can be performed at room temperature.

In addition to the above etchants and etching methods mentioned for usein either the final release or in an intermediate etching step, thereare others that may also be used by themselves or in combination. Someof these include wet etches, such as ACT, KOH, TMAH, HF (liquid); oxygenplasma, SCCO₂, or super critical CO₂ (the use of super critical CO₂ asan etchant is described in U.S. patent application Ser. No. 10/167,272,which is incorporated herein by reference). However, spontaneous vaporphase chemical etchants are more preferred, because the sacrificialmaterial, such as amorphous silicon within small spaces, (such aslateral gap 242 (between the mirror plate and the hinge) and small gap240 (between the substrate and the mirror plate) in FIG. 13) can beefficiently removed via gaps between adjacent mirror plates and thelateral gap as compared to other sacrificial materials (e.g. organicmaterials) and other etching methods. Though not required in allembodiments of the present invention, a micromirror array with a smallgap, a small pitch and a small distance between the hinge and the mirrorplate can thus be more easily fabricated with such spontaneous vaporphase chemical etchants.

Referring to FIG. 11, a flow chart shows the steps executed in anexemplary etching process for removing the sacrificial material(amorphous silicon). The etching process starts at a breakthroughetching (step 254) in breakthrough etching chamber (272 in FIG. 12) ofan etching system for removing the oxidation layers on the surfaces ofthe micromirror. This etching step may lasts for tens of seconds. In apreferred embodiment of the invention, the micromirror is breakthroughetched around 30 seconds. The micromirror is then loaded into theetching chamber (e.g. 278 in FIG. 12) of the etching system for etchingthe sacrificial materials. One or more vapor phase etchants are prepared(step 258) in the building chamber (e.g. 274 in FIG. 12) for vaporizingthe etchants and the expansion chamber (e.g. 276 in FIG. 12) for settingthe vapor phase etchants to a certain pressure. The expanded vapor phaseetchants are then pumped into (step 258) the etching chamber (e.g.etching chamber 278 in FIG. 12). The micromirror is then etched in theetching chamber for a time preferably around 1200 seconds so as tothoroughly remove the sacrificial materials. The etching of themicromirror in the etching chamber may be performed with an end-pointdetection technique for real-timely monitoring the etching process inthe etching chamber. In particular, a residual gas analyzer, whichanalyzes the gas from the etching chamber, is preferably used. Theresidual gas analyzer measures the chemical components and the densityof certain component (it can also measure the density variation rate ofthe certain component) of the gas from the etching chamber. From themeasurements, the amount of sacrificial material inside the etchingchamber may be derived. With the end-point detection, over-etching andincomplete etching may be avoided. When the etching in the etchingchamber is finished (the sacrificial material is removed from themicromirror), the etching chamber is cleaned by pumping out the gasesinside the etching chamber (step 262). The etched micromirror is thenunloaded from the etching chamber (step 264). As an optional feature ofthe embodiment, the micromirror after etching is coated with aself-assembled-monolayer (SAM) for protecting the micromirror (e.g. froma trichlorosilane or trialkanesilane precursors). The SAM coating isperformed at steps 264 through 270. Following step 263, wherein themicromirror is unloaded from the etching chamber, the micromirror isloaded into the SAM chamber (e.g. SAM chamber 280 in FIG. 12) (step264). The SAM material is then pumped into the SAM chamber (step 266).The micromirror inside the SAM chamber is exposed to the SAM materialfor around 60 seconds, and coated with the SAM materials thereby.Finally, the micromirror is unloaded from the SAM chamber (step 270).

It will be appreciated by those of ordinary skill in the art that a newand useful spatial light modulator and a method of fabricating thespatial light modulator have been described herein. In view of manypossible embodiments to which the principles of this invention may beapplied, however, it should be recognized that the embodiments describedherein with respect to the drawing figures are meant to be illustrativeonly and should not be taken as limiting the scope of invention. Forexample, those of ordinary skill in the art will recognize that theillustrated embodiments can be modified in arrangement and detailwithout departing from the spirit of the invention. In particular, themicromirrors and the electrode and circuitry can be formed on the samesubstrate. Also, though PVD and CVD are referred to above, other thinfilm deposition methods could be used for depositing the layers,including spin-on, sputtering, anodization, oxidation, electroplatingand evaporation. Therefore, the invention as described hereincontemplates all such embodiments as may come within the scope of thefollowing claims and equivalents thereof.

1. A method, comprising: forming first and second sacrificial layerswith a plurality of hinges formed in a hinge layer on one of the firstand second sacrificial layers and with an array of mirror plates formedin a mirror plate layer on the other of the first and second sacrificiallayers; wherein the mirror plates are formed with a gap between adjacentmirror plates of from 0.15 to 0.5 micrometers; wherein one of the firstand second sacrificial layers is between the mirror plate layer andhinge layer and has a thickness of from 0.15 to 1.5 micrometers; forminga hinge support on the second sacrificial layer for each mirror platefor supporting the mirror plate; and removing at least a portion of oneor both of the first and the second sacrificial layers using aspontaneous vapor phase chemical etchant.
 2. The method of claim 1,wherein a center-to-center distance between adjacent mirror plates isfrom 4.38 to 10.16 micrometers.
 3. The method of claim 1, wherein thearray of mirror plates comprises at least 1280 mirror plates along alength of the array.
 4. The method of claim 1, wherein the array ofmirror plates comprises at least 1400 mirror plates along a length ofthe array.
 5. The method of claim 1, wherein the array of mirror platescomprises at least 1600 mirror plates along a length of the array. 6.The method of claim 1, wherein the array of mirror plates comprises atleast 1920 mirror plates along a length of the array.
 7. The method ofclaim 1, wherein the step of removing the first and second sacrificiallayers further comprises: removing the first sacrificial layer using thespontaneous vapor phase chemical etchant via the gap between adjacentmirror plates.
 8. The method of claim 1, wherein the gap is from 0.15 to0.25 micrometers.
 9. The method of claim 1, wherein the gap is from 0.25to 0.5 micrometers.
 10. The method of claim 1, wherein the gap is 0.5micrometers or less.
 11. The method of claim 1, wherein the thickness ofthe second sacrificial layer is from 0.5 to 1.5 micrometers.
 12. Themethod of claim 1, wherein the thickness of the second sacrificial layeris from 0.8 to 1.25 micrometers.
 13. The method of claim 1, wherein thethickness of the second sacrificial layer is from 0.95 to 1.15micrometers.
 14. The method of claim 1, wherein a center-to-centerdistance between adjacent mirror plates is from 8.07 to 10.16micrometers.
 15. The method of claim 1, wherein a center-to-centerdistance between adjacent mirror plates is from 6.23 to 9.34micrometers.
 16. The method of claim 1, wherein a center-to-centerdistance between adjacent mirror plates is from 4.38 to 6.57micrometers.
 17. The method of claim 1, wherein a center-to-centerdistance between adjacent mirror plates is from 4.38 to 9.34micrometers.
 18. The method of claim 1, further comprising: forming thehinge for the mirror plates such that, after removing the first andsecond sacrificial layer, a) the mirror plate can rotate relative to thesubstrate along a rotation axis that is parallel to but offset from adiagonal of the mirror plate when viewed from the top of the mirrorplate; and b) the mirror plate can rotate to an angle at least 14degrees relative to the substrate; and wherein the step of forming thearray of mirror plates on the first sacrificial layer further comprises:forming the array of mirror plates on the first sacrificial layer suchthat adjacent mirror plates have a gap from 0.15 to 0.5 micrometerstherebetween.
 19. The method of claim 1, wherein the step of forming ahinge support on the second sacrificial layer for each mirror platefurther comprises: forming a hinge for the mirror plate such that, afterremoving the first and second sacrificial layer, the mirror plate canrotate above the substrate to a rotation angle at least 14° degreesrelative to the substrate.
 20. The method of claim 1, furthercomprising: forming an electrode for each mirror plate; and disposingthe electrode proximate to the mirror plate for electrostaticallydeflecting the mirror plate.
 21. The method of claim 1, wherein thesubstrate is glass or quartz that is visible light transmissive.
 22. Themethod of claim 20, further comprising: depositing an anti-reflectionfilm on a surface of the substrate.
 23. The method of claim 20, furthercomprising: depositing a light absorbing frame around an edge of thesubstrate.
 24. The method of claim 1, wherein the step of removing thefirst and second sacrificial layer further comprises: monitoring anendpoint of the sacrificial layer being removed using a residual gasanalyzer.
 25. The method of claim 1, wherein the first sacrificial layeror the second sacrificial layer comprises amorphous silicon.
 26. Themethod of claim 1, wherein the spontaneous vapor phase etchant is aninterhalogen.
 27. The method of claim 1, wherein the spontaneous vaporphase etchant is HF.
 28. The method of claim 1, wherein the spontaneousvapor phase etchant is a noble gas halide.
 29. The method of claim 28,wherein the noble gas halide comprises xenon difluoride.
 30. The methodof claim 26, wherein the interhalogen comprises bromine trichloride orbromine trifluoride.
 31. The method of claim 1, wherein a diluent ismixed with the vapor phase etchant during removing the first and secondsacrificial layer.
 32. The method of claim 31, wherein the diluent isselected from N₂, He, Ar, Kr and Xe.
 33. The method of claim 31, whereinthe diluent is selected from N₂ and He.
 34. The method of claim 1,wherein each mirror plate has an area; and wherein a ratio of asummation of the areas of all mirror plates of the mirror plate array toan area of the substrate is 90 percent or more.
 35. The method of claim1, wherein each mirror plate rotates relative to the substrate inresponse to an electrostatic force.
 36. The method of claim 1, furthercomprising: disposing a first electrode proximate to each mirror platefor electrostatically driving the mirror plate to rotate in a firstdirection relative to the substrate; and disposing a second electrodeproximate to the mirror plate for electrostatically driving the mirrorplate to rotate in a second direction opposite to the first directionrelative to the substrate.
 37. The method of claim 36, wherein the firstelectrode and the second electrode are disposed on the same siderelative to a rotation axis of the mirror plate.
 38. The method of claim36, wherein the first electrode and the second electrode are disposed onthe opposite sides relative to a rotation axis of the mirror plate. 39.The method of claim 1, wherein the substrate is semiconductor.
 40. Themethod of claim 1, wherein the step of forming the hinge support on thesecond sacrificial layer for each mirror plate further comprises:forming a hinge for the mirror plate such that, after removing the firstand second sacrificial layer, the mirror plate can rotate in a firstdirection to an angle from 15° degrees to 27° degrees relative to thesubstrate.
 41. The method of claim 40, wherein the step of forming thehinge support on the second sacrificial layer for each mirror platefurther comprises: forming a hinge for the mirror plate such that, afterremoving the first and second sacrificial layer, the mirror plate canrotate in a second direction opposite to the first direction to an anglefrom 2° degrees to 9° degrees relative to the substrate.
 42. The methodof claim 1, wherein the step of forming the hinge support on the secondsacrificial layer for each mirror plate further comprises: forming ahinge for the mirror plate such that, after removing the first andsecond sacrificial layer, the mirror plate can rotate in a firstdirection to an angle from 17.5° degrees to 22.5° degrees relative tothe substrate.
 43. The method of claim 42, wherein the step of formingthe hinge support on the second sacrificial layer for each mirror platefurther comprises: forming a hinge for the mirror plate such that, afterremoving the first and second sacrificial layer, the mirror plate canrotate in a second direction opposite to the first direction to an anglefrom 2° degrees to 9° degrees relative to the substrate.
 44. The methodof claim 1, wherein the step of forming the hinge support on the secondsacrificial layer for each mirror plate further comprises: forming ahinge for the mirror plate such that, after removing the first andsecond sacrificial layer, the mirror plate can rotate in a firstdirection to an angle around 20° degrees relative to the substrate. 45.The method of claim 44, wherein the step of forming the hinge support onthe second sacrificial layer for each mirror plate further comprises:forming a hinge for the mirror plate such that, after removing the firstand second sacrificial layer, the mirror plate can rotate in a seconddirection opposite to the first direction to an angle from 2° degrees to9° degrees relative to the substrate.
 46. The method of claim 1, whereinthe step of forming the hinge support on the second sacrificial layerfor each mirror plate further comprises: forming a hinge for the mirrorplate such that, after removing the first and second sacrificial layer,the mirror plate can rotate in a first direction to an angle around 30°degrees relative to the substrate.
 47. The method of claim 46, whereinthe step of forming the hinge support on the second sacrificial layerfor each mirror plate further comprises: forming a hinge for the mirrorplate such that, after removing the first and second sacrificial layer,the mirror plate can rotate in a second direction opposite to the firstdirection to an angle from 2° degrees to 9° degrees relative to thesubstrate.
 48. The method of claim 11, further comprising: forming thehinge for the mirror plate such that, after removing the first andsecond sacrificial layer, the mirror plate can rotate in a firstrotation direction to an angle from 12° degrees to 20° degrees relativeto the substrate.
 49. The method of claim 48, further comprising:forming the hinge for the mirror plate such that, after removing thefirst and second sacrificial layer, the mirror plate can rotate in asecond rotation direction opposite to the first rotation direction to anangle from 2° degrees to 9° degrees relative to the substrate.
 50. Themethod of claim 2, further comprising: forming the hinge for the mirrorplate such that, after removing the first and second sacrificial layer,the mirror plate can rotate in a first rotation direction to an anglefrom 12° degrees to 20° degrees relative to the substrate.
 51. Themethod of claim 50, further comprising: forming the hinge for the mirrorplate such that, after removing the first and second sacrificial layer,the mirror plate can rotate in a second rotation direction opposite tothe first rotation direction to an angle from 2° degrees to 9° degreesrelative to the substrate.